Calculate sum of certain observations in a group

[Jaeyong Yoo]

Hello,

I want to calculate the sum of only certain categories' value in a group. Here is a part of the sample (I randomly chose the numbers).

Family	Person	Income
1	1	100
1	2	110
1	3	130
2	1	50
2	2	60
2	3	70
2	4	80
3	1	40
3	2	50

In Family 1, there are three family members; in Family 2, four family members; and in Family 3, two members.

I want to calculate the sum of Person 1 and 2's income. So, for Family 1, it should be 100+110 = 220 and for Family 2, 50+60=110.


I want to create this below data set:

Family	Person	Income	Income_1_2
1	1	100	210
1	2	110	210
1	3	130	210
2	1	50	110
2	2	60	110
2	3	70	110
2	4	80	110
3	1	40	90
3	2	50	90

I tried to use this code, but I don't know how to make conditions.
bys Family: egen Income_1_2 = total(Income)

Thank you in advance.

[Andrew Musau]

* Example generated by -dataex-. To install: ssc install dataex
clear
input byte(family person) int income
1 1 100
1 2 110
1 3 130
2 1  50
2 2  60
2 3  70
2 4  80
3 1  40
3 2  50
end

bys family(person): egen wanted=total(cond(inlist(person, 1,2), income, .))

Res.:

. l, sepby(family)

     +-----------------------------------+
     | family   person   income   wanted |
     |-----------------------------------|
  1. |      1        1      100      210 |
  2. |      1        2      110      210 |
  3. |      1        3      130      210 |
     |-----------------------------------|
  4. |      2        1       50      110 |
  5. |      2        2       60      110 |
  6. |      2        3       70      110 |
  7. |      2        4       80      110 |
     |-----------------------------------|
  8. |      3        1       40       90 |
  9. |      3        2       50       90 |
     +-----------------------------------+

.

[Jaeyong Yoo]

Thank you Andrew. That is exactly what I want.

[Joro Kolev]

Another way would be

. bysort family (person): egen totinc = total(income/(_n<3))

. list, sepby(family)

     +-----------------------------------+
     | family   person   income   totinc |
     |-----------------------------------|
  1. |      1        1      100      210 |
  2. |      1        2      110      210 |
  3. |      1        3      130      210 |
     |-----------------------------------|
  4. |      2        1       50      110 |
  5. |      2        2       60      110 |
  6. |      2        3       70      110 |
  7. |      2        4       80      110 |
     |-----------------------------------|
  8. |      3        1       40       90 |
  9. |      3        2       50       90 |
     +-----------------------------------+

[Nick Cox]

#4 The help for egen warns against using _n in calls to that command. A safer tweak would be one of

bysort family : egen totinc = total(income / (person <= 2)) 

bysort family : egen totinc = total(income / inlist(person, 1, 2))

For more on the approaches in #2 and #4 see Sections 9 and 10 respectively of https://www.stata-journal.com/articl...article=dm0055